The present invention relates generally to substrate processing, and more particularly to the transfer of substrates to and from processing chambers.
Glass substrates are being used for applications such as active matrix television and computer displays, among others. Each glass substrate can form multiple display monitors each of which contains more than a million thin film transistors.
The processing of large glass substrates often involves the performance of multiple sequential steps, including, for example, the performance of chemical vapor deposition (CVD) processes, physical vapor deposition (PVD) processes, or etch processes. Systems for processing glass substrates can include one or more process chambers for performing those processes.
The glass substrates can have dimensions, for example, of 550 mm by 650 mm. The trend is toward even larger substrate sizes, such as 650 mm by 830 mm and larger, to allow more displays to be formed on the substrate or to allow larger displays to be produced. The larger sizes place even greater demands on the capabilities of the processing systems.
Some of the basic processing techniques for depositing thin films on the large glass substrates are generally similar to those used, for example, in the processing of semiconductor wafers. Despite some of the similarities, however, a number of difficulties have been encountered in the processing of large glass substrates that cannot be overcome in a practical way and cost effectively by using techniques currently employed for semiconductor wafers and smaller glass substrates.
For example, efficient production line processing requires rapid movement of the glass substrates from one work station to another, and between vacuum environments and atmospheric environments. The large size and shape of the glass substrates makes it difficult to transfer them from one position in the processing system to another. As a result, cluster tools suitable for vacuum processing of semiconductor wafers and smaller glass substrates, such as substrates up to 550 mm by 650 mm, are not well suited for the similar processing of larger glass substrates, such as 650 mm by 830 mm and above. Moreover, cluster tools require a relatively large floor space.
Similarly, chamber configurations designed for the processing of relatively small semiconductor wafers are not particularly suited for the processing of these larger glass substrates. The chambers must include apertures of sufficient size to permit the large substrates to enter or exit the chamber. Moreover, processing substrates in the process chambers typically must be performed in a vacuum or under low pressure. Movement of glass substrates between processing chambers, thus, requires the use of valve mechanisms which are capable of closing the especially wide apertures to provide vacuum-tight seals and which also must minimize contamination.
Furthermore, relatively few defects can cause an entire monitor formed on the substrate to be rejected. Therefore, reducing the occurrence of defects in the glass substrate when it is transferred from one position to another is critical. Similarly, misalignment of the substrate as it is transferred and positioned within the processing system can cause the process uniformity to be compromised to the extent that one edge of the glass substrate is electrically non-functional once the glass has been formed into a display. If the misalignment is severe enough, it even may cause the substrate to strike structures and break inside the vacuum chamber.
Other problems associated with the processing of large glass substrates arise due to their unique thermal properties. For example, the relatively low thermal conductivity of glass makes it more difficult to heat or cool the substrate uniformly. In particular, thermal losses near the edges of any large-area, thin substrate tend to be greater than near the center of the substrate, resulting in a non-uniform temperature gradient across the substrate. The thermal properties of the glass substrate combined with its size, therefore, makes it more difficult to obtain uniform characteristics for the electronic components formed on different portions of the surface of a processed substrate. Moreover, heating or cooling the substrates quickly and uniformly is more difficult as a consequence of its poor thermal conductivity, thereby reducing the ability of the system to achieve a high throughput.
The transportation of substrates between chambers in a processing system is usually automated. To achieve a high throughput, substrates must be transported between chambers as quickly as possible. However, substrates, must be placed with great accuracy in order to be processed correctly. Consequently, sudden acceleration or deceleration of the substrate during transport may jar and misalign it. For example, jittering or vibration caused by a drive mechanism, or a sudden impact when the substrate is transferred from one drive mechanism to another, can misalign or even damage the substrate, thereby reducing process yield.
Another problem in substrate transport is contamination. Specifically, the drive mechanism may generate particles that contaminate the substrate, thereby causing defects that reduce process yield.
In one aspect, the invention is directed to an apparatus for performing a thin film fabrication process on a substrate. The apparatus has a first chamber, a second chamber in communication with the first chamber, a substrate support moveable along a path between the first chamber and the second chamber, and a magnetic drive including a first magnetic surface to generate a first magnetic field and a second magnetic surface to generate a second magnetic field. The first magnetic surface is magnetically engageable with the second magnetic surface so that movement of the second magnetic field causes the support to move along the linear path.
Implementations of the invention may include the following. Movement of the second magnetic field may be caused by modifying the current flowing through electromagnets in an electromagnetic drive assembly, or by movement of the second magnetic surface. The first magnetic surface may be located on the support, and the second magnetic surface may be located outside a process environment of the first and second chambers. A rotatable pinion may have the second magnetic surface. The rotatable pinion may be located outside an evacuable chamber. The path between the first and second chambers may be generally linear.
The support may include a plurality of linearly-spaced magnets, and a rotatable pinion may have a plurality of pinion magnets. The pinion magnets and the linearly-spaced magnets can magnetically engage so that rotation of the pinion will cause the support to move along the path. A magnetic levitation assembly may magnetically levitate the substrate support. The guide rollers can contact an upper and a lower surface of the support. The linearly-spaced magnets may be along at least one side of the support. Guide rollers may also be positioned to engage at least one side of the support.
The pinion magnets may include a first set of magnets having a first polarity interleaved with a second set of magnets having a second polarity. The linearly-spaced magnets may include a third set of magnets with the second polarity interleaved with a fourth set of magnets with the first polarity. The pinion and linearly-spaced magnets may be positioned such that the first and third sets of magnets can magnetically couple and the second and fourth sets of magnets can magnetically couple. The first and second pluralities of magnets may have magnetic axes that are oriented substantially radially, and the third and fourth pluralities of magnets may have magnetic axes that are orientated substantially perpendicular to the axis of rotation of the pinion. The pinion may be located between the first and second chambers.
A third chamber may be in communication with the second chamber, and a second rotatable pinion may be located between the second and third chambers. The second pinion may include a second plurality of pinion magnets. The support may be moveable along a second path between the second chamber and the third chamber, and the second plurality of pinion magnets and the linearly-spaced magnets can magnetically engage so that rotation of the second pinion will cause the support to move along the second linear path. A first motor may rotate the first pinion and a second motor may rotate the second pinion. A control system synchronizes the operation of the first and second motors.
Each rack magnet and each pinion magnet may be a plate. Each plate may be oriented at an angle xcex1, e.g., between about 0xc2x0 and 45xc2x0, between a primary axis of the plate and an axis of rotation of the pinion.
The shuttle may have first and second pluralities of rack magnets located along opposite sides of the shuttle, and there may be a first rotatable pinion having a first plurality of pinion magnets and a second rotatable pinion having a second plurality of pinion magnets. The first plurality of pinion magnets can magnetically engage the first plurality of rack magnets and the second plurality of pinion magnets can magnetically engage the second plurality of rack magnets, so that rotation of the first and second pinions causes movement of the shuttle along the linear path. A first motor may drive the first pinion. A second motor may drive the second pinion, or a drive shaft may connect the first pinion and the second pinion.
The substrate support may be a substrate transfer shuttle. A plurality of linearly-spaced magnets may be on one side of the shuttle, e.g., in a rack. A rotatable pinion having a plurality of pinion magnets may be positioned adjacent the one side of the shuttle. A second plurality of linearly-spaced magnets, e.g., in a second rack, may be positioned on an opposite side of the shuttle, and a second rotatable pinion having a second plurality of pinion magnets may be positioned adjacent the opposite side of the shuttle.
In another aspect, the invention is directed to a substrate transport apparatus. The substrate transport apparatus includes a transfer shuttle moveable along a generally path and including a plurality of linearly-spaced magnets, and a rotatable pinion having a plurality of pinion magnets. The pinion magnets and the linearly-spaced magnets can magnetically engage so that rotation of the pinion will cause the shuttle to move along the path.
In another aspect, the invention is directed to a method of transporting a substrate between chambers of a fabrication system. In the method, a substrate is supported on a substrate support that has a plurality of linearly-spaced magnets and that is moveable along a path between a first chamber and a second chamber. A pinion having a plurality of pinion magnets is rotated so that the pinion magnets and the linearly-spaced magnets magnetically engage to move the substrate support along the path.
Advantages of the invention may include the following. Substrates, particularly large glass plates, may be transported smoothly and quickly between chambers with smooth acceleration and deceleration, and with little jittering, jarring, or vibration. Particle generation by the drive mechanism is minimized, thereby reducing defects and increasing process yield.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.